Method and apparatus for distinguishing harmless surface flaws from dangerous fissures in magnetizable bodies



Jan. 13, 1959 c. w. MCKEE ETAL METHOD AND APPARATUS FOR DISTINGUISHINGHARMLE SURFACE FLAWS FROM DANGEROUS FISSURES IN MAGNETIZABLE BODIES-Filed March 9, '19s:

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METHOD AND APPARATUS FOR DISTINGUISHING HARMLESS SURFACE FLAWS FROMDANGEROUS FISSURES IN MAGNETIZABLE BODIES- Filed March 9, 1953 v 4Sheets-Sheet 2 GAUGE 66 68 22 711 N81 39 A n n n V U U U 1' 4;.- piaaJ85 230 178 17g 180 BELL D E y vpu U" STAVGEQ J 5TA6'E *3 255112 VOUTPUT fi iag I J86 1A5 J75 172 179 INVENTORS.

c. w. M KEE ET AL 2,869,073

G HARMLESS SURES Jan. 13, 1959 METHOD AND APPARATUS F OR DISTINGUISHINSURFACE FLAWS FROM DANGEROUS FIS IN MAGNETIZABLE BODIES Om 9% 02 mm QQWQ2 \M Q2 Q2 1 OZ NQ l m9 v WNX a2 NW 02 09 WWX l 3 QT OZ ESL um mwmwimew 3595 Q3 mp3 Nu on a RA INVENTORS 01/ Jan. 13, 1959 c. w. MGKEE ET AL2,369,073

1 METHOD AND APPARATUS FOR DISTINGUISHING HARMLESS SURFACE FLAWS FROMDANGEROUS FISSURES IN MAGNETIZABLE BODIES Filed March 9, 1953 4Sheets-Sheet 4 GAU i -"if I h. \EXTENT OF F/SSURE FIELD LEAD TURNS 0FCOIL 198- 206 A REAR- TURN5 0F can. 198* 212 LEAD TURNS 0F COIL 200i A210 216 REAR TURNS 0F can. 200 1 22? Campos/TE SIGNAL 1 RECEIVED ATFIRST --V- M STAGE OF AMPLIFIER 220 INVENTOR C 6 66 228 BY A UnitedStates Patent Chester W. McKee, Hoinewood, and Richard W. McKee,.Highland Park, llh, assignors, by mesne assignments, to Teleweld, Inc.,a corporation of Idaho Appiication March 9, 1953, Serial No. 340,944 4Claims. (Cl. 324-37) This invention relates to an improved method andapparatus for distinguishing harmless surface flaws from dangerousdefects in magnetizable bodies. It will be particularly useful insegregating signals derived from hardened portions of a magnetic body.Its success is closely dependent upon the use of a sustained magneticfield in which a flux-responsive means is operating. Inasmuch as theinvention stems from an observation made during rail testing, applicantswill describe the figures of the drawings, and then describe theexperiment.

Fig. l is a schematic side elevation of a Teledetector fissure detectorcar;

Fig. 2 is a side elevation of a rail illustrating applicants sustainedflux field pattern;

Fig. 3 is a side elevation of a rail indicating flux patterns from ashell and a fissure in a residually magnetized rail;

Fig. 4 is a side elevation of a rail ball indicating flux patterns froma shell and a fissure in a sustained magnetic field;

Fig. 5 is a plan view of the top of a portion of a rail showingschematically the positioning of applicants coils thereabove;

Fig. 6 shows typical graphs of a fissure potential signal and a shellpotential signal derived by applicants apparatus;

Fig. 7 sets forth two hypothetical tapes and compares the resultsobtained by full wave rectification as compared with half waverectification in conjunction with a sustained field;

Fig. 8 is a wiring diagram of applicants pickup circuit and amplifier;

Fig. 9 is a composite arrangement of a side elevation of a rail, a planView of a rail, and graphs of potential signals for the purpose ofsuggesting a reason why applicants invention functions;

Fig. 10 is a graph of a fissure potential signal seen on an oscilloscopeconnected to the Teledetector apparatus; and,

Fig. 11 is a graph of a shell potential signal seen on an oscilloscopeconnected to the Teledetector apparatus.

In detecting dangerous defects, whether internal or surface, inmagnetizable bodies, the first step is to explore a magnetic fieldadjacent a body with a flux-responsive means as rapidly as possible. Forexample, in testing a new rail in a rolling mill, the flux-responsivemeans will be moved along a rail in either a sustained or a residualfield and if it produces a potential of a selected amplitude, a check ofthat portion of the rail producing the. magnetic field will be made.Because the rail is new and does not have in its surface shells, flowsand wheel burns, the detecting apparatus can be adjusted to a highdegree of efficiency. The surface contour of the new rail ball isreasonably uniform with the result that the detection apparatus can bemade responsive almost exclusively to the type of signal derived from adangerous defect. The same holds true inthe checking of new pipe andother factory-madearticles of steel. An im- 2,869,073 patented Jan. is,1959 portant field for fissure detection work, however, is in checkingmagnetizable bodies which have been used. In the case of rails in track,the uniform contour of the ball no longer exists. ,It is broken by railjoints, wheel burns, shells and flows, all of which are harmless, butall of which produce distortions in the magnetic field adjacent the railwhich in turn produce potential signals in the flux-responsive means.The same is true of such material as oil well drill pipe, which uponremoval from the ground may have slight indentations due to blows or theteeth of a wrench or a collet of a rotary drill.

These surface. defects render what is called the exploratory step offissure detection work inaccurate. A potential signal derived from adistorted magnetic field created by a shell may have the same amplitudeas a potential signal derived from a flux field created by a fissure,and consequently, the visual portrayals of these potential signals willnot have such distinctive significanoe as to enable an observer toseparate dangerous fissures from harmless surface defects This is a veryold problem infissure detection work and hundreds of patents have issuedon pickup coils, positioning the pickupcoils, connecting the pickupcoils, amplifier circuits, suppressors and visual presentation means,all directed toward. assisting the operator in distinguishing theharmless from the .dangerous flaws, in the first instance. Whereheisunable to inake this distinction with confide-ncein the first instance,he is obliged to make close visual examination or a hand check of thatportion of the magnetizable bodyfrom which the potential signal wasderived. The hand checking of harmless flaws, or more commonly thevisual examination of the exterior of a mag netizable body to confirm.that a visual signal came from a harmless defect, is a major item infissure detection service. In: the case of testingrail in track, eachstop of the exploratory car consumes several minutes. Inasmuch as thesecars must test about thirty miles of track in .a seven-hour day in orderto be commercially practical, and inasmuch as there is only about onedangerous fissure in every thirty or fortymiles of. track which ischecked at intervals of three to six months, it is evident that theability to distinguish the harmless from the dangerouswfissures in thefirst instance, that is, when the detector car is moving at ten totwelve miles an .hour along the track, is of crucial importance.

Applicants are the designers of what is known in the trade astheTeledetector fissure detector car. A study of the tapes made by this caron the north rail of the Pocatello, Idaho, test track of the UnionPacific Railroad resulted in an. observation which had never been madebefore, although the applicants had been working on, the presentTeledetector sustained field system for several years. In ordertoappreciate the observation, it is necessary to understand ratherspecifically the Teledetector apparatus in use at the time that theexperiment occurred,

TheTeledetector car, referring to Fig. 1 is a 60- to 70- foot motor car10 mounted on a forward motor truck 12 and a trailing truck 14. In theforward end, is a drivers. cab 16 and at the rear is a fissure detectoroperators cab 18. Generatorsprovide power fordriving, the car along therail and functioning the magnets, amplifiers and visual presentation;means. The latter usually consists of two, batteries of pens, one foreach rail, writing on a tape moving approximately two inches for each 39feet of rail traversed. Beneath the car are three magnet trucks 20, .22a;nd124, each having vertically positionedelectrically energizedmagnets. While the car is moving, there is a sustained magnetic fieldfollowing .the dotted lines 26. At 1the point where the flux lines leavetherail at substantially right angles to the ball of. the rail, therelis nositio e a fiu spqns m an '2 w c Campinas.

a plurality of pairs of coils having non-magnetic cores.

This is the point where a dip needle stands somewhat vertically and itoccurs between the two wheels primarily because of the spacing of therear magnetic truck 24 from them. The output of each pair of coils ofthe fluxresponsive means 28 is carried to a separate amplifier 30 whichin turn functions a separate pen unit 32. Whenever a coil is movingthrough a field in which the number of force lines cut is increasing, apositive potential will be induced in the coil; and conversely, wheneverit is moving through a field in which the number of lines of flux isdecreasing, a negative potential will be induced in the coil.

Theorizing on the functioning of fissure detection apparatus has notproved very satisfactory in the past. However, it is likely that theobservation which applicants made would be true only of aflux-responsive means operating at a fixed position in a movingsustained field and hence the general nature of such a field should beunderstood. In Fig. 2, applicants show the rear portion of the magnetcarried by the truck 24. This magnets lower pole has a north polarityadjacent to the rail. When energized, it pushes out into the rail linesof flux which leave the rail along the dotted lines such as 36. One pairof opposed connected, longitudinally aligned coils, in cross section(much enlarged), is indicated by the numeral 38 positioned in that partof the field where a dip needle 40 stands substantially vertically. Thefluxresponsive means 38 is at a fixed distance behind the magnets.Assuming for a moment that one has a perfect rail and that the assemblyis moved from right to left, the flux pattern in the air remains exactlythe same. It is just as if nothing moved. Now, assuming that there is ashell, which is a surface defect 42, as the flux field moves to theleft, the pattern of the lines of flux immediately adjacent that defectis altered. The density and the direction of the flux is different fromthat existing over the normal rail ball. Inasmuch as the coils 38generate only a potential when there is a change in the quantity of theflux or in the direction of the flux passing through them, it is evidentfirstly that the coils 38 will generate some kind of a potential signalas they move over the defect. All that the coils 38 check are changes inthe quantity and direction of the lines of flux coming out of the railimmediately beneath the coils, that is, in the area between the twoarrows 44 and 46.

Further as to the nature of the flux field above a rail, in Fig. 3 therail has been residually magnetized, that is, a magnetizing force hasbeen moved along the rail ball to a point where it no longer exerts anyappreciable effect on the field around the rail. The numeral 48indicates a shell, above which is suggested the closed lines of flux 50as they would appear in a residual field. A shell is a portion of a railwhich has become hardened.- The steel in a shell has a higher reluctancethan a normal portion of a rail. Its color is dark. It may extend alongthe gauge side wall of the ball for several inches and occasionallyextends on the top of the ball as far as the median line thereof. Thenumeral 52 identifies an internal fissure. The faces of the internalfissure in the rail have opposite polarities so that if the left side 54is north, the right side 56 is south. The residual flux field in the airabove the fissure will be as indicated by the dotted lines 58.

In a sustained field, however, the concepts of the flux fieldsmodifiedby defects are quite different. Here the powerful magnet 24, see Fig. 4,having a north pole adjacent to the rail is lining up the molecules andholding them as indicated by the arrows, wherein the head of each arrowindicates a north pole. When this sustained field flux patternencounters a shell 49, the lines of flux are concentrated around theperimeter of the shell. In the center ofthe shell, the number of linesof flux are comparatively few. When this sustained field flux patternencounters'an internal fissure 63, there isa concentration of flux 66 onthe lead side of the fissure, and 'a.

to traverse a field 67 of subnermal intensity.

selected amplitude is received.

' into the last stage is positive.

less than normal quantity of flux 67 on the trailing side of thefissure. N

Continuing to refer to Fig. 4, the pickup 64, which is moving to theleft, leaves a field of normal intensity It next threads the much denserfield 66, after which it re-enters the normal flux field 61. Thepotential signal induced in the coils by the fissure sustained fluxfield will therefore be negative, strong positive, and negative. Intraversing the sheel field 66, on the other hand, the pickup 64 movesfrom a normal flux field into a more dense, next into a very subnormal69 in the center of the shell, and then back into a normal field. Thepotential signal induced in the coil by the shell field will thereforebe first positive, and then strongly negative, and then positive. Intraversing the shell field, there may be many reversals in the directionof the lines of flux, but the important fact is that the low densitysustained flux field above the shell produces a high amplitude negativecomponent.

The pickup coils of the Teledetector car on this particular test werethree effective pairs. See copending application Serial No. 256,502,filed November 15, 1951, now Patent No. 2,766,425, of which thisapplication is a continuation in part. Their full size and position overthe rail is shown in Fig. 5. The numeral 66 identifies the ball of therail, having a gauge side 63 and a field side 70. The flux-responsivemeans is a non-magnetic block 72 having vertical, cylindrical cavitiesinto which are dropped pairs of coils connected in opposed relationship.The gauge pair of coils 74, the center pair 76, and the field pair 78are all identical. The two dotted lines 80 and 82 indicate the outer andinner limits of the windings on each coil. Each pair of coils has onelead grounded and the other is connected to a separate amplifier whichin turn functions a separate pen unit. The three pen units write on thesame tape 132, see Fig. 7, the gauge pen being designated No. l; thecenter pen, No. 2; and the field pend, No. 3.

The Teledetector car checked the north rail of the Pocatella test track.This test track contains ten fissures ranging in size from eight percentto fifteen percent and approximately twenty shells. The tape recordedeight of the fissures and thirteen shells. The applicants connected oneamplifier to an oscilloscope and they studied the potential signaldelineation of all thirteen shell signals and eight fissure signals. InFig. 6, applicants sketch side by side a shell signal 83 and a fissuresignal 81, typical of those studied. While the amplitude of the eightfissure signals differed and the duration of the signal differedslightly, all of the fissure signals had one common characteristic,namely, that the high amplitude potential generated was positive. In thecase of the shell potential signals, they had one common characteristicand that was that the high amplitude signal was always negative.

In the Teledetector apparatus at that time, there was a twin diode orfull wave rectification stage, the output of which converts allpotential signals received by that stage, whether negative or positive,into positive signals. The output stage of the amplifier functions arelay which in turn functions the pen unit whenever a signal of aimportantly, the Teledetector apparatus has its stages so arranged thatthe signal Upon observing that the high potential signal derived fromthe fissure field was of a polarity opposite to the high potentialsignal of the shell, the applicants removed the full wave rectificationstage in the amplifier and amplified only signals of that polarity whichwas the same as that of the high amplitude component of a fissurepotential signal.

With this change, the rail was again checked. The results wereoutstandingly successful. One fissure field wrote on all three pens,five wrote on Nos. 1 and 2- pens, and four wrote on No. 1 pen. Everyfissure was caught. Not a single shell field wrote on both Nos. 1

The No. l pen is connected to the gauge coil, the No. 2 to the centercoil, and the No. 3 tothe field coil. Inasmuch as the shellsare almostalways physically beneath the gauge and center coils, the operator wassaved at least eight shell inspections. I In order that the advantage ofthis arrangement may be more clearly perceived, applicants have made uptwo hypothetical tapes positioned next to a hypothetical rail containingthreefissures and six shells. This is shown in Fig. 7. The rail ball 84,shown out ofproportion, is illustrated as part ofa track in which jointbars 86 connect the rail 84 to rails 88 and 90. The three dotted lines92, 94 and 96 indicate difierent size internal fissures in the rail. Thegroups of dots 98, 100, 102, 104 and 106 indicate different size shellson the gaugeside 108 of the rail. The flux-responsive means 110 containsthe three pairs of coils, the gauge pair 112 connected through anamplifier 114 to No. 1 or gauge pen 116; the center pair 118 connectedthrough an amplifier 120 to the No. 2 pen 122; and the field pair 124connected through the amplifier 126 to the N0. 3 pen 128. Assuming thatthe flux-responsive means .124 is moving inthedirection of the arrow130, the pens typically would have written the tape 132 when theTeledetector car was employing full wave rectification. At the joints,all three pens write 134. The first shell wrote on two pens 136. Thefirst fissure wrote on the same two pens 138. The small shell 1'00 wroteon No. l pen 140. The shell-102 wrote on two pens 142. The small fissure94 wrote on none of the pens. The large fissure 96 wrote on all threepens. The shell 104 wrote on No. l pen only, 144. The shell 105 wrote onno pens. The large shell 106' wrote on all pens 146.

In the column to the right of thetape 132 headed Is a Stop Indicated,applicants have indicated the correct and 2 pens.

answer in view of the tape, assuming that the detector operator was notlooking out of his window to observe the presence of a shell on therail. The correct answers call for five stops. From the standpoint ofdangerous fissures, only two of these five stops should have been madeand one stop, that is, for fissure 94, was not re quired.

The tape 148 is a hypothetical tape showing the results of running thecar Without full wave rectification over the same rail. This tape iscomparable to the long tape made on the test track. On this tape, thereare only four signals that came through. It should be borne in mind thatthe amplification had been slightly stepped up on the second running ofthe track in order to catch the small fissure 94. The signals 150 and152 indicated to the operator clearly that a stop must be made. Theother two signals 154 from thesmall fissure 94 and 156 from the largeshell 106 are substantially the same. Assuming that the operator couldnot see the track, he would have to stop both times. In practice,however, the operator is looking out the car window and the large shellis clearly visible. When he received the fissure signal 154 and saw nodeformation of the rail, he would give the signal to stop. When hereceived the signal 156 and then saw the large shell, he would not givea signal to stop.

Comparing the two tapes, on the tape 132, the operator would havestopped twice for the fissures 92 and 96. And he probably woud havepassed the shells 98, 102 and 106 because he could see them on the rail..Had he increased the amplification so as to bring upthe small fissure94, the shells 98 and 100 would probably have recorded on the third pen.The tape 148 .is vastly superior. It makes it possible to maintain theamplification at a sufficiently high point so that the smallest fissurewill produce a signal in atleast one pen while at the same time reducingthe number of shell signals which actuate the pen. The cleanness of thetape is important firstly because it is not confusing to the operator,but also because the tape is delivered to the railroad which will checkit against a subsequent service failure.

Describing now the specific hookup employed by the applicants, andreferring to Fig. 8, 158 is a section throughthe north pole of avertically positioned magnet immediately adjacent a rail 160. Positionedabove the rail rearwardly of the magnet are two coils wound onvertically positioned non-magnetic cores. The coils, one-half tothree-quarters of an inch in diameter, are Wound identically the same.The inside lead of the leading coil 162 is connected by a conductor 164to the first stage 166 of applicants amplifier. The outer lead of theleading coil 162 is connected by a conductor 168 to the outer. lead ofthe second coil 170. The inner lead of the coil 170 is grounded.Commencing. with the conductor 164, the circuits are diagrammatic only.Actually, the circuits are quite complex and vary for particularinstallations. The signal is carried through several amplificationstages to a differentiating stage which is the fourth stage and bearsthe numeral 172. Here it is again phase inverted and with the highamplitude component of the fissure potential signal now positive, 180,the signal enters the output stage. The tube in this stage 182 is sobiased (standard practice) that itbecomes conductive only upon receivinga positive potential signal. Negative components 179 do not affect thisoutput stage. They are lost. Only the positive signal 180 actuates thepen unit 184 or the bell .185.

Applicants early'in this disclosure indicated that the. polarity of thehigh potential component in a shell potential signal was opposite to thehigh potential component of a fissure potential signal because thenumber of lines of flux within the sustained field passing through theshell and back up to the magnet were comparatively few. Establishing thetruth of this simple explanation is difficult, in part because of thenature of the fluxrespon sive means. Applicants two coils on verticalaxes positioned one behind the other are connected in opposedrelationship and the lead turns on one coil. will produce apotentialsignal of the opposite polarity to the trailing turns of the same coil.Nevertheless, applicants have laid out Fig. 9 for the purpose ofexplaining What actually occurs.

Referring to Fig. 9, a side elevation of the ball 192 of a rail 188 isshown above and therebelow the top of the same rail ball. A fissure 194isi ndicated by dash lines. The magnet is to the right and is movingfrom left to right. The pickup coil is to the left of the fissure 194and consists of the two coils 198 and 2&0. The spacing of the linesoffiux bracketed by the numerals 189 and 191 indicates the density ofthe flux flowing from perfect rail. The fissure 194 constitutes anobstacle to the flow of flux from the magnets and there is aconcentration of flux 1% in the magnetside of the rail. Resultingly,

there is substantially les-flux flowing from the rail on the pickup sideof the fissure, the lines being bracketed and indicated by the numeral193. The shell 224, being composed of harder steel, presents an obstacleto the flow of flux at the surface of the rail and much of the flux thatnormally would leave that portion of the rail is pushed over to theedgesof the shell. The arrows 226, in the side elevation of the ball 192.,show a heavy density of flux. However, referring to the plan view, thedots indicate lines of flux and it will be seen that the lines of fluxat 226 are denser than in the normal portion of the rail 191 and thatthe lines of fiux within the shell itself are much fewer than the numberin the normal portion of the rail 191.

it is evident that as these coils leave the normal field 189 and enterthe less dense field 1%, their overall output will be a negativepotential. As they traverse the dense field 196, their.over-allpotential will be strongly positive. Upon leaving this dense filed andreturning tothe normal field 191, the cells will, produce a negativepotential. 1 t t 7 The coils 198 and 200 probably would pass the shell224 without producing an appreciable signal. However, the gauge coils,suggested by the coil 203, would pass over the shell. These coils 203would produce a typical fissure signal-minus, strongly plus, minusintraversing the field above the fissure 194. As they leave the normalflux field 191, they would first encounter an increase in the number oflines of flux, then a decrease in the number of lines of flux cut, andfinally an increase. The signal would be plus, strongly minus, thenplus.

At the bottom of Fig. 9, applicants have indicated the composite signalreceived at the first stage of the amplifier 166 by the pickup coils asthey traverse first the fissure, the signal bearing the numeral 220, andthen the shell, the signal bearing the numeral 228. The high rate ofchange of the shell signal is indicated by the portion 226 of the signal228. This also is a composite of impulses received by the pickup coils.

Continuing to refer to Fig. 9, the applicants have suggested how thelead and rear turns of the coils may reinforce each other. The diagramindicates how the lead turns at first produce. a negative signal 204followed by a positive signal 206; how the rear turns of the lead coil198 produce a positive signal 208 which partly overlaps the positivesignal of the lead turns of the same coil. The lead turns of the coil200 which is connected in opposed relationship with the coil 198 thenproduce a positive impulse which overlap in point of time the impulsesinduced by the other parts of the pickup circuit. The signals 212, 214,216 and 218 occur in point of time so that they do not overlap. Signals206, 208 and 210 may be additive to produce the large signal 230. Thissame effect undoubtedly occurs in the case of-the shell. The spacing ofthe lead and rear turns of'each coil and the spacing of the coils fromeach other Will affect the potential signal that reaches the first stageof the amplifier.

In making the connections between the pickup coils and the amplifier,two things are important. Firstly, the polarity of the large componentof the fissure detector signal such as 230 must be known. Secondly, thatpolarity must be positive when it reaches the output stage 182. Thislatter can readily be accomplished by selecting the appropriate numberof stages in the amplifier. Ordinarily, the polarity of a signal isreversed as it passes through each stage. The graphs of the signal as itmoves through the amplifier are schematically shown between the stagesin Fig. 8. The right result is obtained because there are five stages inthe amplifier and the large component 230 is positive as it enters thefirst stage. If the connections to the pair of pickup coils arereversed, that is, the dot-dash connections 184 and 186 were used, theproper result would be obtained by adding or subtracting one stage inthe amplifier. It is evident that the critical element is the polarityof the large component of the fissure detector signal, for in applicantssustained field system of detection, that polarity will always heopposite to the polarity of the large component of a surface defectsignal.

The operability of applicants method and apparatus is dependent uponhaving the positive signal enter the output stage only because of thenature of that stage. That stage contains a tube which becomesconductive so as to operate a pen relay only when a signal of positivepolarity is received by the stage. It is possible to design a stage inwhich a negative signal received at the input of the stage would aloneestablish an operating circuit through the output conductor of thatstage.

A detailed wiring diagram of the amplifier has not been included becauseit bears no important relationship to the invention here disclosed.There have been slight adjust rnents of otentiometers and the insertionor withdrawal of condensers, all of which have improved the function ingof the device. But the basic idea resides in the elimination of fullwave rectification in a flux-responsive 55 means testing or threading auni-directional sustained field Applicants uni-directional trailingsustained field induces into the pickup coils a potential signal from afissure field having a large component of a polarity opposite to thepolarity of the large component of a signal derived from a shell. I g

It is important that too much weight not be given to the fact that thecomponent of the fissure signal having the high amplitude appears as thesecond component in the schematic illustration in Fig. 9. The applicantsare not certain that the large component has the same or the oppositepolarity of the initial component in the fissure signal. As illustratedin Figs. 10' and 11, some tests indicate that the large component ofeither the fissure or the shell is the third and not the secondcomponent. The important thing is that the polarity of the largecomponent of the fissure field is opposite to the polarity of the largecomponentof the shell, burn, flow or other surface defect creatingclosed fields.

The high speed in performing the exploratory step is becomingincreasingly important in fissure detection work because of theincreasing amount of controlled cooled rail in track. Controlled cooledrail does not develop fissures generated by shatter cracks within theball. This had always been the primary source of internal fissures.Prior to the controlled cooled rail, the rails were cooled at the millin air. The surface cooled first and established stress locks. As theinterior of the rail cooled, it established its own stress locks. Theresult was stresses in a rail ball which repeated blows from wheelswould release so as to start an internal fissure. As controlled cooledrails leave a mill, they are stacked white hot in an insulated railroadgondola and covered. Cooling requires from two days to a week. Theresult is that stress locks have been nearly eliminated. In thesecontrolled cooled rails, internal fissures develop primarily from slaginclusions. At any event, the number of fissures developed isdecreasing. The result is that many more miles of track must be testedfor each fissure found. This makes it necessary to perform theexploratory step faster and more accurately.

Having thus described their claim:

1. The method of operating that type of apparatus for segregatinginternal fissures from harmless surface defects in magnetizable objectswhich equipment includes (a) a magnet having one pole positioned closeto the magnetizable object with the other pole spaced verticallythereabove so as to create a flux field of lines of force leaving theobject at an acute angle, said field being formed by flux moving fromthe first pole through a portion of the object and then outwardlythrough its surface and the field to the other pole; (b) aflux-responsive means sufficiently short so that in moving through saidflux field adjacent the surface of the object and distorted by aninternal fissure major changes in flux density .will generate in a leadto the flux-responsive means potentials of opposite polarity; (c)signal-producing means apprehendible by the human senses and capableofdistinguishing between signals of opposite polarity; and (0!) meansfor rendering the apparatus responsive to signalsof just one polarity,which comprises the steps of magnetizing the objects so that surfaceflux fields aifected by internal fissures will have characteristicallydifierent flux patterns from those from surface defects, of moving theflux-responsive means through these fields and determining the polarityof the major potential received from a flux field modified by a knowninternal fissure, and of setting the apparatus to render, apprehendiblesignals of that polarity and that polarity only.

2. The method of operating that type of apparatus for segregatinginternal fissures from harmless surface defects in magnetizable objectswhich equipment includes (a) a magnet having one pole positioned closeto the magnetizable object with the other pole spaced verticallyinvention, applicants thereabove so as to create a flux field of linesof force leaving the object at an acute angle, said field being formedby flux moving from the first pole through a portion of the object, andthen outwardly through its surface and the field to the other pole; (b)a coil disposed on a vertical axis and suificiently short so that inmoving through said flux field adjacent the surface of the object anddistorted by an internal fissure major changes in flux density willgenerate in a lead to the coil potentials of opposite polarity;signal-producing means apprehendible by the human senses and capable ofdistinguishing between signals of opposite polarity; and (d) means forrendering the apparatus responsive to signals of just one polarity,which comprises the steps of magnetizing the object so that surface fluxfields aifected by internal fissures will have characteristicallydifferent fiux patterns from thosefrom surface defects, of moving thecoil through these fields and determining the polarity of the majorpotential received from a flux field modified by a known internalfissure, and of connecting the leads of the coil to thesignal-producingmeans so that only signals of the polarity of the major potential of theflux field modified by the internal fissure actuate the signal producingmeans.

3. The method of operating that type of apparatus for segregatinginternal fissures from harmless surface defects in magnetizable objectswhich equipment includes (a) a magnet having one pole positioned closeto the magnetizable object with the other pole spaced verticallythereabove so as to create a flux field of lines of force leavingtheobject at an acute angle, said field being formed by flux moving fromthe first pole through a portion of the object, and then outwardlythrough its surface and the field to the other pole; (b) aflux-responsive means sutficiently short so that in moving through saidflux field adjacent the surface of the object and distorted by aninternal fissure major changes in flux density will generate in a leadto the flux-responsive means potentials v of opposite polarity; (c)signal-producing means appre hendible by the human senses and capable ofdistinguishing between signals of opposite polarity; and (d) means forrendering the apparatus responsive to signals of just one polarity,which comprises the steps of magnetizing the object so thatunidirectional flux flows outwardly into the space through which theflux-responsive means is to pass thereby creating flux fields adjacentinternal fissures characteristically different from those adjacentsurface defects, of moving the flux-responsive means through thesefields and determining the polarity of the major potential received froma flux field modified by a known internal fissure, and of setting theapparatus to render apprehendible signals of that polarity and thatpolarity only.

4. The method of operating that type of apparatus for segregatinginternal fissures from harmless surface defects in magnetizable objectswhich equipment includes (a) a magnet having one pole positioned closeto the magnetizable object with the other pole spaced verticallythereabove so as to create a flux field of lines of force leaving theobject at an acute angle, said field being formed by flux moving fromthe first pole through a portion of the object, and then outwardlythrough its surface and the field to the other pole; (b) a coil disposedon a vertical axis and sufiiciently short so that in moving through saidflux field adjacent the surface of the object and distorted by aninternal fissure major changes in flux density will generate in a leadto the coil potentials of opposite polarity; (c) signal-producing meansapprehendible by the human senses and capable of distinguishing betweensignals of opposite polarity; and (d) means for rendering the apparatusresponsive to signals of just one polarity, which comprises the steps ofmagnetizing the object so that unidirectional flux flows outwardly intothe space through which the coil is to pass therebyvcreating flux fieldsadjacent internal fissures characteristically difierent from thoseadjacent surface defects, of moving the coil through these fields anddetermining the polarity of the major potential received from a fluxfield modified by a known internal fissure, and connecting the leads ofthe coil to the signal-producing means so that only signals of thepolarity of the major potential of the flux field modified by theinternal fissure actuate the signalproducing means.

References Cited in the file of this patent UNITED STATES PATENTS2,461,252 Barnes et a1 Feb. 8, 1949 2,461,253 Barnes et al.- Feb. 8,1949 2,571,998 Barnes et al. Oct. 23, 1951 2,571,999 Barnes et al Oct.23, 1951 2,602,108 Dionne July 1, 1952 2,614,154 Dionne Oct. 14, 19522,624,779 Keaton et a1. Jan. 6, 1953 2,639,316 McKee et a1 May 19, 19532,671,197 Barnes et a1. Mar. 2, 1954 2,729,785 Keevil Jan. 3, 1956

